mixed-signal test and dft
DESCRIPTION
Mixed-Signal Test and DFT. Vishwani D. Agrawal Agere Systems, Murray Hill, NJ 47974 [email protected] http://cm.bell-labs.com/cm/cs/who/va May 17, 2001. VLSI Realization Process. Customer’s need. Determine requirements. Write specifications. Design synthesis and Verification. - PowerPoint PPT PresentationTRANSCRIPT
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Mixed-Signal Test and DFT
Mixed-Signal Test and DFT
Vishwani D. AgrawalAgere Systems, Murray Hill, NJ 47974
[email protected]://cm.bell-labs.com/cm/cs/who/va
May 17, 2001
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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VLSI Realization ProcessVLSI Realization Process
Determine requirements
Write specifications
Design synthesis and Verification
FabricationManufacturing test
Chips to customer
Customer’s need
Test development
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Costs of TestingCosts of Testing Design for testability (DFT)
Chip area overhead and yield reduction Performance overhead
Software processes of test Test generation and fault simulation Test programming and debugging
Manufacturing test Automatic test equipment (ATE) capital cost Test center operational cost
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Cost of Manufacturing Testing in 2000AD
Cost of Manufacturing Testing in 2000AD
0.5-1.0GHz, analog instruments,1,024 digital pins: ATE purchase price = $1.2M + 1,024 x $3,000 = $4.272M
Running cost (five-year linear depreciation) = Depreciation + Maintenance + Operation
= $0.854M + $0.085M + $0.5M = $1.439M/year
Test cost (24 hour ATE operation) = $1.439M/(365 x 24 x 3,600) = 4.5 cents/second
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Characterization TestCharacterization Test
Worst-case test Choose test that passes/fails chips Select statistically significant sample of
chips Repeat test for every combination of 2+
environmental variables Plot results in Schmoo plot Diagnose and correct design errors
Continue throughout production life of chips to improve design and process to increase yield
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Manufacturing TestManufacturing Test
Determines whether manufactured chip meets specs
Must cover high % of modeled faults Must minimize test time (to control cost) No fault diagnosis Tests every device on chip Test at speed of application or speed
guaranteed by supplier
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Burn-in or Stress TestBurn-in or Stress Test
Process: Subject chips to high temperature &
over-voltage supply, while running production tests
Catches: Infant mortality cases – these are
damaged chips that will fail in the first 2 days of operation – causes bad devices to actually fail before chips are shipped to customers
Freak failures – devices having same failure mechanisms as reliable devices
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Test Specifications & PlanTest Specifications & Plan Test Specifications:
Functional Characteristics Type of Device Under Test (DUT) Physical Constraints – Package, pin
numbers, etc. Environmental Characteristics – supply,
temperature, humidity, etc. Reliability – acceptance quality level
(defects/million), failure rate, etc. Test plan generated from specifications
Type of test equipment to use Types of tests Fault coverage requirement
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Automatic Test Equipment Components
Automatic Test Equipment Components Consists of:
Powerful computer Powerful 32-bit Digital Signal
Processor (DSP) for analog testing Test Program (written in high-level
language) running on the computer Probe Head (actually touches the bare
or packaged chip to perform fault detection experiments)
Probe Card or Membrane Probe (contains electronics to measure signals on chip pin or pad)
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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ADVANTEST Model T6682 ATE
ADVANTEST Model T6682 ATE
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Test Process SummarizedTest Process Summarized
Parametric tests – determine whether pin electronics system meets digital logic voltage, current, and delay time specs
Functional tests – determine whether internal logic/analog sub-systems behave correctly
ATE Cost Problems Pin inductance (expensive probing) Multi-GHz frequencies High pin count (1024)
ATE Cost Reduction Multi-Site Testing DFT methods like Built-In Self-Test
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Mixed-Signal Testing Problem
Mixed-Signal Testing Problem
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Differences from Digital Testing
Differences from Digital Testing
Size not a problem – at most 100 components Much harder analog device modeling
No widely-accepted analog fault model Infinite signal range Tolerances depend on process and
measurement error Tester (ATE) introduces measurement error Digital / analog substrate coupling noise Absolute component tolerances +/- 20%,
relative +/- 0.1% Multiple analog fault model mandatory
No unique signal flow direction
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Present-Day Analog Testing Methods
Present-Day Analog Testing Methods
Specification-based (functional) tests Main method for analog – tractable and
does not need an analog fault model Intractable for digital -- # tests is huge
Structural ATPG – used for digital, just beginning to be used for analog (exists)
Separate test for functionality and timing not possible in analog circuit Possible in digital circuit
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Waveform SynthesisWaveform Synthesis
Needs sin x / x (sinc) correction – Finite sample width
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Waveform SamplingWaveform Sampling
Sampling rate > 100 ks/s
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A/D and D/A Test Parameters
A/D and D/A Test Parameters
A/D -- Uncertain map from input domain voltages into digital value (not so in D/A) Two converters are NOT inverses
Transmission parameters affect multi-tone tests Gain, signal-to-distortion ratio,
intermodulation distortion, noise power ratio, differential phase shift, envelop delay distortion
Intrinsic parameters – Converter specifications Full scale range (FSR), gain, # bits, static
linearity (differential and integral), maximum clock rate, code format, settling time (D/A), glitch area (D/A)
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Ideal Transfer Functions
Ideal Transfer Functions
A/D Converter D/A Converter
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D/A Transfer Function Non-Linearity Error
D/A Transfer Function Non-Linearity Error
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Differential Linearity Error
Differential Linearity Error
Differential linearity function – How each code step differs from ideal or average step (by code number), as fraction of LSB
Subtract average count for each code tally, express that in units of LSBs
Repeat test waveform 100 to 150 times, use slow triangle wave to increase resolution
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Linear Histogram and DLE of 8-bit ADC
Linear Histogram and DLE of 8-bit ADC
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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DSP-Based TestingDSP-Based Testing DSP-based tester has:
Waveform Generator Waveform Digitizer High frequency clock with dividers for
synchronization A/D and D/A Test Parameters
Transmission Intrinsic
A/D and D/A Faults: offset, gain, non-linearity errors Measured by DLE, ILE, DNL, and INL
A/D Test Histograms – static linear and sinusoidal D/A Test –- Differential Test Fixture
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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DSP-Based Test Concepts
DSP-Based Test Concepts
Quantization Error – Introduced into measured signal by discrete sampling
Quantum Voltage – Corresponds to flip of LSB of converter
Single-Tone Test -- Test of DUT using only one sinusoidal tone
Tone – Pure sinusoid of f, A, and phase Transmission (Performance) Parameter --
indicates how channel with embedded analog circuit affects multi-tone test signal
UTP – Unit test period: joint sampling period for analog stimulus and response
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Spectral Test of A/D Converter
Spectral Test of A/D Converter
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Spectral Components in DSP-Based Testing
Spectral Components in DSP-Based Testing
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A/D Converter Spectrum
A/D Converter Spectrum
Audio source at 1076 Hz sampled at 44.1 kHz
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Coherent Multi-Tone Testing
Coherent Multi-Tone Testing
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Analog Test BusAnalog Test Bus PROs:
Usable with digital JTAG boundary scan Adds analog testability – both controllability and
observability Eliminates large area needed for analog test points
CONs: May have a 5 % measurement error C-switch sampling devices couple all probe points
capacitively, even with test bus off – requires more elaborate (larger) switches
Stringent limit on how far data can move through the bus before it must be digitized to retain accuracy
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Analog Test Bus DiagramAnalog Test Bus Diagram
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Analog Boundary ModuleAnalog Boundary Module
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Chaining of 1149.4 ICsChaining of 1149.4 ICs
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Partitioning for TestPartitioning for Test
Partition according to test methodology: Logic blocks Memory blocks Analog blocks
Provide test access: Boundary scan Analog test bus
Provide test-wrappers (also called collars) for cores.
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Test-Wrapper for a Core
Test-Wrapper for a Core
Test-wrapper (or collar) is the logic added around a core to provide test access to the embedded core.
Test-wrapper provides: For each core input terminal
A normal mode – Core terminal driven by host chip An external test mode – Wrapper element observes core
input terminal for interconnect test An internal test mode – Wrapper element controls state of
core input terminal for testing the logic inside core For each core output terminal
A normal mode – Host chip driven by core terminal An external test mode – Host chip is driven by wrapper
element for interconnect test An internal test mode – Wrapper element observes core
outputs for core test
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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A Test-WrapperA Test-Wrapper
Wrappertest
controller
Scan chain
Sca
n c
hain
Sca
n c
hain
to/from TAP
from/toExternalTest pins
Wrapperelements
Core
Fun
ctio
nal
core
in
pu
ts
Fun
ctio
nal
core
ou
tpu
ts
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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Overhead EstimateOverhead Estimate
Rent’s rule: For a logic block the number of gates Gand the number of terminals t are related by
t = K G
where 1 < K < 5, and ~ 0.5.
Assume that block area A is proportional to G, i.e.,t is proportional to A 0.5. Since test logic is addedto each terminal t,
Test logic added to terminals
Overhead = ------------------------------------------------- ~ A –0.5
A
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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DFT Architecture for SOC
DFT Architecture for SOC
User defined test access mechanism (TAM)
Module
1Test
wra
pper
Testsource
Testsink
Module
NTest
wra
pper
Test access port (TAP)
Functionalinputs
FunctionaloutputsFunc.
inputs
Func.outputs
SOC inputs SOC outputsTD
I
TC
K
TM
S
TR
ST
TD
O
Instruction register control
Serial instruction data
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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DFT ComponentsDFT Components
Test source: Provides test vectors via on-chip LFSR, counter, ROM, or off-chip ATE.
Test sink: Provides output verification using on-chip signature analyzer, or off-chip ATE.
Test access mechanism (TAM): User-defined test data communication structure; carries test signals from source to module, and module to sink; tests module interconnects via test-wrappers; TAM may contain bus, boundary-scan and analog test bus components.
Test controller: Boundary-scan test access port (TAP); receives control signals from outside; serially loads test instructions in test-wrappers.
May 17, 2001 Mixed-Signal Test and DFT: [email protected]
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SummarySummary Functional test: verify system hardware, software,
function and performance; pass/fail test with limited diagnosis; high (~100%) software coverage metrics; low (~70%) structural fault coverage.
Diagnostic test: High structural coverage; high diagnostic resolution; procedures use fault dictionary or diagnostic tree.
SOC design for testability: Partition SOC into blocks of logic, memory and analog
circuitry, often on architectural boundaries. Provide external or built-in tests for blocks. Provide test access via boundary scan and/or analog
test bus. Develop interconnect tests and system functional tests. Develop diagnostic procedures.